Many implantable medical devices have been coated with various types of coatings, such as coatings for delivering a therapeutic agent or drug to a site within the body, coatings for radiopacity, or coatings for biocompatibility. One example of a drug-coated implantable medical device is a stent, which is a tubular structure formed in a mesh-like pattern that is designed to be inserted into an organ or vessel and serve as a scaffolding. For example, a stent may be placed in a coronary artery across an area of blockage that has been opened by an angioplasty procedure. In many instances, however, the stented area becomes blocked again (known as restenosis) due to various biological processes, including tissue healing and regeneration, scar formation, irritation, and immune reactions that lead to an excess proliferation of the cells. Therefore, many stents are coated with a drug, such as paclitaxel or other therapeutic agent, that acts to inhibit the processes that cause restenosis.
Various methods have been proposed or employed for coating stents and other medical devices. Such methods include spray coating, dip coating, etc. These methods have various advantages and disadvantages. For example, some spray coating methods result in a large amount of coating being wasted. Spray deposition efficiencies are important as coating materials (e.g., a drug and polymer matrix) have become more expensive. As another example, some coating methods are slow and result in lengthy and costly production. As another example, some coating methods result in non-uniform coatings or fail to apply sufficient coating to certain surfaces. It is often desirable to apply the coating in a uniform manner to ensure that an intact, robust coating of the desired thickness is formed. Some of these drawbacks are trade-offs in certain coating processes. For example, in order to achieve the desired uniformity and completeness of the coating in a spray coating process, stents are commonly spray coated individually, with each stent separately loaded onto a stent holder and then separately spray coated. This individual handling can slow the production rate.
The present invention is directed to an improvement to overcome certain drawbacks in prior coating systems.